Dopant profile control in gate structures for semiconductor devices

ABSTRACT

A semiconductor device with different gate structure configurations and a method of fabricating the same are disclosed. The semiconductor device includes a fin structure disposed on a substrate, and first and second gate structures on the fin structure. The first and second gate structures includes first and second interfacial oxide layers, respectively, first and second high-K gate dielectric layers disposed on the first and second IO layers, respectively, and first and second dopant control layers disposed on the first and second HK gate dielectric layers, respectively. The second dopant control layer has a silicon-to-metal atomic concentration ratio greater than an Si-to-metal atomic concentration ratio of the first dopant control layer. The semiconductor further includes first and second work function metal layers disposed on the first and second dopant control layers, respectively, and first and second gate metal fill layers disposed on the first and second work function metal layers, respectively.

BACKGROUND

With advances in semiconductor technology, there has been increasingdemand for higher storage capacity, faster processing systems, higherperformance, and lower costs. To meet these demands, the semiconductorindustry continues to scale down the dimensions of semiconductordevices, such as metal oxide semiconductor field effect transistors(MOSFETs), including planar MOSFETs and fin field effect transistors(finFETs). Such scaling down has increased the complexity ofsemiconductor manufacturing processes.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of this disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the common practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1A, 1B-1I, 1V-1W, and 1J-1U illustrate an isometric view,cross-sectional views, and device characteristics of a semiconductordevice with different gate structures, in accordance with someembodiments.

FIG. 2 is a flow diagram of a method for fabricating a semiconductordevice with different gate structures, in accordance with someembodiments.

FIGS. 3A-6B, 7A-7F, and 8A-12B illustrate cross-sectional views of asemiconductor device with different gate structures at various stages ofits fabrication process, in accordance with some embodiments.

FIGS. 6C and 11C-11E illustrate device characteristics of asemiconductor device with different gate structures at various stages ofits fabrication process, in accordance with some embodiments.

Illustrative embodiments will now be described with reference to theaccompanying drawings. In the drawings, like reference numeralsgenerally indicate identical, functionally similar, and/or structurallysimilar elements.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the processfor forming a first feature over a second feature in the descriptionthat follows may include embodiments in which the first and secondfeatures are formed in direct contact, and may also include embodimentsin which additional features may be formed between the first and secondfeatures, such that the first and second features may not be in directcontact. As used herein, the formation of a first feature on a secondfeature means the first feature is formed in direct contact with thesecond feature. In addition, the present disclosure may repeat referencenumerals and/or letters in the various examples. This repetition doesnot in itself dictate a relationship between the various embodimentsand/or configurations discussed.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper,” and the like may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. The spatially relative termsare intended to encompass different orientations of the device in use oroperation in addition to the orientation depicted in the figures. Theapparatus may be otherwise oriented (rotated 90 degrees or at otherorientations) and the spatially relative descriptors used herein maylikewise be interpreted accordingly.

It is noted that references in the specification to “one embodiment,”“an embodiment,” “an example embodiment,” “exemplary,” etc., indicatethat the embodiment described may include a particular feature,structure, or characteristic, but every embodiment may not necessarilyinclude the particular feature, structure, or characteristic. Moreover,such phrases do not necessarily refer to the same embodiment. Further,when a particular feature, structure or characteristic is described inconnection with an embodiment, it would be within the knowledge of oneskilled in the art to effect such feature, structure or characteristicin connection with other embodiments whether or not explicitlydescribed.

It is to be understood that the phraseology or terminology herein is forthe purpose of description and not of limitation, such that theterminology or phraseology of the present specification is to beinterpreted by those skilled in relevant art(s) in light of theteachings herein.

As used herein, the term “etch selectivity” refers to the ratio of theetch rates of two different materials under the same etching conditions.

As used herein, the term “high-k” refers to a high dielectric constant.In the field of semiconductor device structures and manufacturingprocesses, high-k refers to a dielectric constant that is greater thanthe dielectric constant of SiO₂ (e.g., greater than 3.9).

As used herein, the term “low-k” refers to a low dielectric constant. Inthe field of semiconductor device structures and manufacturingprocesses, low-k refers to a dielectric constant that is less than thedielectric constant of SiO₂ (e.g., less than 3.9).

As used herein, the term “p-type” defines a structure, layer, and/orregion as being doped with p-type dopants, such as boron.

As used herein, the term “n-type” defines a structure, layer, and/orregion as being doped with n-type dopants, such as phosphorus.

As used herein, the term “nanostructured” defines a structure, layer,and/or region as having a horizontal dimension (e.g., along an X- and/orY-axis) and/or a vertical dimension (e.g., along a Z-axis) less than,for example, 100 nm.

As used herein, the term “n-type work function metal (nWFM)” defines ametal or a metal-containing material with a work function value closerto a conduction band energy than a valence band energy of a material ofa FET channel region. In some embodiments, the term “n-type workfunction metal (nWFM)” defines a metal or a metal-containing materialwith a work function value less than 4.5 eV.

As used herein, the term “p-type work function metal (pWFM)” defines ametal or a metal-containing material with a work function value closerto a valence band energy than a conduction band energy of a material ofa FET channel region. In some embodiments, the term “p-type workfunction metal (pWFM)” defines a metal or a metal-containing materialwith a work function value equal to or greater than 4.5 eV.

In some embodiments, the terms “about” and “substantially” can indicatea value of a given quantity that varies within 5% of the value (e.g.,±1%, ±2%, ±3%, ±4%, ±5% of the value). These values are merely examplesand are not intended to be limiting. It is to be understood that theterms “about” and “substantially” can refer to a percentage of thevalues of a given quantity as interpreted by those skilled in relevantart(s) in light of the teachings herein.

As used herein, the term “multi-threshold voltage (multi-Vt) device”defines a semiconductor device with two or more FETs, where each of thetwo or more FETs have a threshold voltage different from each other.

The fin structures disclosed herein may be patterned by any suitablemethod. For example, the fin structures may be patterned using one ormore photolithography processes, including double-patterning ormulti-patterning processes. Generally, double-patterning ormulti-patterning processes combine photolithography and self-alignedprocesses, allowing patterns to be created that have, for example,pitches smaller than what is otherwise obtainable using a single, directphotolithography process. For example, in some embodiments, asacrificial layer is formed over a substrate and patterned using aphotolithography process. Spacers are formed alongside the patternedsacrificial layer using a self-aligned process. The sacrificial layer isthen removed, and the remaining spacers may then be used to pattern thefin structures.

The required gate voltage—the threshold voltage (Vt)—to turn on a fieldeffect transistor (FET) can depend on the semiconductor material of theFET channel region and/or the effective work function (EWF) value of agate structure of the FET. For example, for an n-type FET (NFET),reducing the difference between the EWF value(s) of the NFET gatestructure and the conduction band energy of the material (e.g., 4.1 eVfor Si or 3.8 eV for SiGe) of the NFET channel region can reduce theNFET threshold voltage. For a p-type FET (PFET), reducing the differencebetween the EWF value(s) of the PFET gate structure and the valence bandenergy of the material (e.g., 5.2 eV for Si or 4.8 eV for SiGe) of thePFET channel region can reduce the PFET threshold voltage. The EWFvalues of the FET gate structures can depend on the thickness and/ormaterial composition of each of the layers of the FET gate structure. Assuch, FETs can be manufactured with different threshold voltages byadjusting the thickness and/or material composition of the FET gatestructures.

Due to the increasing demand for multi-functional portable devices,there is an increasing demand for FETs with different threshold voltageson the same substrate. One way to achieve such multi-Vt device can bewith different work function metal (WFM) layer thicknesses in the FETgate structures. However, the different WFM layer thicknesses can beconstrained by the FET gate structure geometries. For example, ingate-all-around (GAA) FETs, the WFM layer thicknesses can be constrainedby the spacing between the nanostructured channel regions of the GAAFETs. Also, depositing different WFM layer thicknesses can becomeincreasingly challenging with the continuous scaling down of FETs (e.g.,GAA FETs and/or finFETs).

The present disclosure provides example multi-Vt devices with FETs(e.g., GAA FETs and/or finFETs) having threshold voltages different fromeach other and provides example methods of forming such FETs on the samesubstrate. The example methods form NFETs and PFETs with WFM layer ofsimilar thicknesses or without WFM layers, but with different thresholdvoltages on the same substrate. These example methods can be morecost-effective (e.g., cost reduced by about 20% to about 30%) andtime-efficient (e.g., time reduced by about 15% to about 20%) inmanufacturing reliable FET gate structures with different thresholdvoltages than other methods of forming FETs with similar channeldimensions and threshold voltages on the same substrate. In addition,these example methods can form FET gate structures with much smallerdimensions (e.g., thinner gate stacks) than other methods of formingFETs with similar threshold voltages.

In some embodiments, NFETs and PFETs with different gate structureconfigurations, but with similar WFM layer thicknesses can beselectively formed on the same substrate to achieve threshold voltagesdifferent from each other. The different gate structures can have dopantcontrol layers of different compositions disposed on high-K (HK) gatedielectric layers. The different dopant control layers can providedifferent concentration profiles of metal dopants in the HK gatedielectric layers of the different gate structure. The different metaldopant concentration profiles can induce dipoles of differentconcentrations at interfaces between the HK gate dielectric layers andinterfacial oxide (IO) layers (referred to as “HK-IO interfaces”). Thedifferent dipole concentrations result in gate structures with differentEWF values and threshold voltages. Thus, tuning the composition of thedopant control layers can tune the EWF values of the NFET and PFET gatestructures, and as a result can adjust the threshold voltages of theNFETs and PFETs without varying their WFM layer thicknesses.

With the use of the dopant control layers in the NFET and PFET gatestructures, the different dipole concentrations at the HK-IO interfacescan be achieved with the HK gate dielectric layers doped with the sameamount of metal dopants. As a result, the method of forming thedipole-based gate structures with the dopant control layers can be lesscomplicated (e.g., fewer processing steps) and time efficient (e.g.,time reduced by about 15% to about 20%) than other methods of formingdipole-based gate structures without the dopant control layers and withHK gate dielectric layers doped with different amounts of metal dopantsfor dipole of different concentrations. In addition, with the use of thedopant control layers, the HK gate dielectric layers of the dipole-basedgate structures can be doped with a smaller amount of metal dopants thanthe HK gate dielectric layers of dipole-based gate structures withoutthe dopant control layers to achieve the same threshold voltage. Thereduction of dopant amounts in the HK gate dielectric layers can improvethe NFET and PFET performance by reducing low frequency noise or 1/fnoise, reducing metal dopant diffusion between adjacent FETs therebyavoiding metal boundary effects, and/or increasing the k-value of the HKgate dielectric layers.

A semiconductor device 100 having NFETs 102N1-102N4 and PFETs102P1-102P4 is described with reference to FIGS. 1A-1U, according tosome embodiments. FIG. 1A illustrates an isometric view of semiconductordevice 100, according to some embodiments. FIGS. 1B, 1D, and 1F-1Hillustrate cross-sectional views along line A-A of semiconductor device100 of FIG. 1A, according to some embodiments. FIGS. 1C, 1E, and 1Iillustrate cross-sectional views along line B-B of semiconductor device100 of FIG. 1A, according to some embodiments. FIGS. 1J-1U illustratedevices characteristics of semiconductor device 100, according to someembodiments. Even though eight FETs are discussed with reference toFIGS. 1A-1U, semiconductor device 100 can have any number of FETs. Thediscussion of elements of NFETs 102N1-102N4 and PFETs 102P1-102P4 withthe same annotations applies to each other, unless mentioned otherwise.The isometric view and cross-sectional views of semiconductor device 100are shown for illustration purposes and may not be drawn to scale.

Referring to FIGS. 1A-1C, NFETs 102N1-102N4 and PFETs 102P1-102P4 can beformed on a substrate 106. Substrate 106 can be a semiconductormaterial, such as silicon, germanium (Ge), silicon germanium (SiGe), asilicon-on-insulator (SOI) structure, and a combination thereof.Further, substrate 106 can be doped with p-type dopants (e.g., boron,indium, aluminum, or gallium) or n-type dopants (e.g., phosphorus orarsenic).

NFETs 102N1-102N4 and PFETs 102P1-102P4 can include fin structures 108₁-108 ₂ extending along an X-axis, epitaxial fin regions 110A-110B, gatestructures 112N1-112N4 and 112P1-112P4, inner spacers 142, and gatespacers 114.

Referring to FIGS. 1B-1C, fin structure 108 ₁ can include a fin baseportion 108A and nanostructured channel regions 120N disposed on finbase portion 108A, and fin structure 108 ₂ can include a fin baseportion 108B and nanostructured channel regions 122P disposed on finbase portion 108B. In some embodiments, fin base portions 108A-108B caninclude a material similar to substrate 106. Nanostructured channelregions 120N can be wrapped around by gate structures 112N1-112N3 andnanostructured channel regions 122P can be wrapped around by gatestructures 112P1-112P3. Nanostructured channel regions 120N and 122P caninclude semiconductor materials similar to or different from substrate106 and can include semiconductor material similar to or different fromeach other.

In some embodiments, nanostructured channel regions 120N can include Si,SiAs, silicon phosphide (SiP), SiC, or silicon carbon phosphide (SiCP)for NFETs 102N1-102N3 and nanostructured channel regions 122P caninclude SiGe, silicon germanium boron (SiGeB), germanium boron (GeB),silicon germanium stannum boron (SiGeSnB), or a III-V semiconductorcompound for PFETs 102P1-102P3. In some embodiments, nanostructuredchannel regions 120N and 122P can both include Si, SiAs, SiP, SiC, SiCP,SiGe, SiGeB, GeB, SiGeSnB, or a III-V semiconductor compound. Thoughrectangular cross-sections of nanostructured channel regions 120N and122P are shown, nanostructured channel regions 120N and 122P can havecross-sections of other geometric shapes (e.g., circular, elliptical,triangular, or polygonal).

Epitaxial fin regions 110A-110B can be grown on fin base portions108A-108B, respectively, and can be source/drain (S/D) regions of NFETs102N1-102N4 and PFETs 102P1-102P4. Epitaxial fin regions 110A-110B caninclude epitaxially-grown semiconductor materials similar to ordifferent from each other. In some embodiments, the epitaxially-grownsemiconductor material can include the same material or a differentmaterial from the material of substrate 106. Epitaxial fin regions 110Aand 110B can be n- and p-type, respectively. In some embodiments, n-typeepitaxial fin regions 110A can include SiAs, SiC, or SiCP. P-typeepitaxial fin regions 110B can include SiGe, SiGeB, GeB, SiGeSnB, aIII-V semiconductor compound, or a combination thereof.

Gate structures 112N1-112N4 and 112P1-112P4 can be multi-layeredstructures. Gate structures 112N1-112N4 can be wrapped aroundnanostructured channel regions 120N and gate structures 112P1-112P4 canbe wrapped around nanostructured channel regions 122P for which gatestructures 112N1-112N4 and 112P1-112P4 can be referred to as“gate-all-around (GAA) structures” or “horizontal gate-all-around (HGAA)structures.” NFETs 102N1-102N4 and PFETs 102P1-102P4 can be referred toas “GAA FETs 102N1-102N4 and 102P1-102P4” or “GAA NFETs 102N1-102N4 andPFETs 102P1-102P4.”

In some embodiments, NFETs 102N1-102N3 and PFETs 102P1-102P3 can befinFETs and have fin regions 120N* and 122P* instead of nanostructureschannel regions 120N and 122P, as shown in FIGS. 1D-1E. Such finFETs102N1-102N3 and 102P1-102P3 can have gate structures 112N1-112N3 and112P1-112P3 disposed on fin regions 120N* and 122P* as shown in FIGS.1D-1E.

Gate structures 112N1-112N3 and 112P1-112P3 can include (i) interfacialoxide (IO) layers 127N1-127N3 and 127P1-127P3, (ii) HK gate dielectriclayers 128N1-128N3 and 128P1-128P3, (iii) second dopant control layers130, (iv) WFM layers 132N-132P, (vii) fluorine-free tungsten (FFW)layers 134, and (viii) gate metal fill layers 135. Gate structures112N1-112N2 and 112P1-112P2 can further include dipole layers131N1-131N2 and 131P1-131P2, respectively, and gate structures112N1-112P1 can further include first dopant control layer layers 129.Though FIGS. 1B-1C show that all the layers of gate structures112N1-112N3 and 112P1-112P3 are wrapped around nanostructured channelregions 120N and 122P, nanostructured channel regions 120N can bewrapped around by at least IO layers 127N1-127N3 and HK gate dielectriclayers 128N1-128N3 to fill the spaces between adjacent nanostructuredchannel regions 120N. As such, nanostructured channel regions 120N canbe electrically isolated from each other to prevent shorting betweengate structures 112N1-112N3 and S/D regions 110A during operation ofNFETs 102N1-102N3. Similarly, nanostructured channel regions 122P can bewrapped around by at least IO layers 127P1-127P3 and HK gate dielectriclayers 128P1-128P3 nanostructured channel regions 120P to electricallyisolated nanostructured channel regions 122P from each other to preventshorting between gate structures 112P1-112P3 and S/D regions 110B duringoperation of PFETs 102P1-102P3.

The discussion of IO layers 127N1-127N3 applies to IO layers127P1-127P3, respectively, unless mentioned otherwise. IO layers127N1-127N3 can be disposed on nanostructured channel regions 120N, andIO layers 127P1-127P3 can be disposed on nanostructured channel regions122P. IO layers 127N1-127N3 can include silicon oxide (SiO₂, SiOH) and athickness ranging from about 0.5 nm to about 1.5 nm. IO layers127P1-127P3 can include silicon oxide (SiO₂, SiOH), silicon germaniumoxide (SiGeO_(x)) or germanium oxide (GeO_(x)) and a thickness rangingfrom about 0.5 nm to about 1.5 nm. In some embodiments, the thickness ofIO layers 127N1-127N2 and 127P1-127P2 can be different from each otherbased on the material composition of first and second dopant controllayers 129-130, respectively.

The discussion of HK gate dielectric layers 128N1-128N3 applies to HKgate dielectric layers 128P1-128P3, respectively, unless mentionedotherwise. HK gate dielectric layers 128N1-128N3 can be disposed onrespective IO layers 127N1-127N3, and HK gate dielectric layers128P1-128P3 can be disposed on respective IO layers 127P1-127P3. Each ofHK gate dielectric layers 128N1-128N3 can have a thickness (e.g., about1 nm to about 3 nm) that is about 2 to 3 times the thickness of IOlayers 127N1-127N3 and can include (i) a high-k dielectric material,such as hafnium oxide (HfO₂), titanium oxide (TiO₂), hafnium zirconiumoxide (HfZrO), tantalum oxide (Ta₂O₃), hafnium silicate (HfSiO₄),zirconium oxide (ZrO₂), and zirconium silicate (ZrSiO₂) and (ii) ahigh-k dielectric material having oxides of lithium (Li), beryllium(Be), magnesium (Mg), calcium (Ca), strontium (Sr), scandium (Sc),yttrium (Y), zirconium (Zr), aluminum (Al), lanthanum (La), cerium (Ce),praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu),gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium(Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), or (iii) acombination thereof.

HK gate dielectric layers 128N1-128N2 can be doped with metals thatinduce the formation of dipole layers 131N1-131N2, and HK gatedielectric layers 128P1-128P2 can be doped with metals that induce theformation of dipole layers 131P1-131P2. Dipole layer 131N1 can beinduced at the interface between HK gate dielectric layer 128N1 and IOlayer 127N1 (also referred to as “HKN1-ION1 interface”), and dipolelayer 131N2 can be induced at the interface between HK gate dielectriclayer 128N2 and IO layer 127N2 (also referred to as “HKN2-ION2interface”) as shown in FIG. 1B. Similarly, dipole layers 131P1-131P2can be induced at the interfaces between HK gate dielectric layers128P1-128P2 and IO layers 127P1-127P2 (also referred to as “HKP1-IOP1interface” and “HKP2-IOP2 interface”) as shown in FIG. 1C. HK gatedielectric layers 128N3-128P3 can be undoped and as a result, may nothave dipole layers at the interfaces between HK gate dielectric layers128N3-128P3 and IO layers 127N3-127P3 (also referred to as “HKN3-ION3interface” and “HKP3-IOP3 interface”) as shown in FIGS. 1B-1C.

In some embodiments, HK gate dielectric layers 128N1-128N2 can be dopedwith (i) a rare-earth metal, such as Lanthanum (La), Yttrium (Y),Scandium (Sc), Cerium (Ce), Ytterbium (Yb), Erbium (Er), Dysprosium (Dy)and Lutetium (Lu); (ii) a metal from group IIA (e.g., magnesium (Mg) orstrontium (Sr)), group IIIA (e.g., aluminum (Al)), group IIIB (e.g.,yttrium (Y)), or group IVB (e.g., zirconium (Zr), hafmium (Hf) ortitanium (Ti)) of the periodic table; or (iii) a combination thereof HKgate dielectric layers 128N1-128N2 can be doped with dopants similar toor different from the dopants of HK gate dielectric layers 128P1-128P2.In some embodiments, HK gate dielectric layers 128N1-128N2 and128P1-128P2 can be doped with La or La₂O₃. In some embodiments, HK gatedielectric layers 128N1-128N2 can be doped with Y, Sr, Lu, La, Y₂O₃,SrO, Lu₂O₃, La₂O₃, or a combination thereof to improve the n-typeperformance of NFETs 102N1-102N2, while HK gate dielectric layers128P1-128P2 can be doped with Ti, Zr, Al₂O₃, TiO₂, ZrO₂, or acombination thereof to improve the p-type performance of PFETs102P1-102P2.

The formation of dipoles from dipole layers 131N1-131N2 and 131P1-131P2depend on the dopants of HK gate dielectric layers 128N1-128N2 and128P1-128P2, respectively. Dipole layers 131N1-131N2 can give rise tospecially charged dipoles of oxygen ions and/or of metal ions fromdopants and/or ions from dopant layers 129-130 and IO layers 127P1-127P2and difference in the oxygen ions density between IO layers 127N1-127N2,dopant metal oxides and HK gate dielectric layer 128N1-128N2. Similarly,dipole layers 131P1-131P2 can give rise to specially charged dipolesarising from migration of metal ions from dopants of HK gate dielectriclayers 128P1-128P2 and/or oxygen ions from IO layers 127P1-127P2 andmetal dopant oxide, and/or metal/metalloid ions from IO layers127P1-127P2. For example, dipole layers 131N1-131N2 and 131P1-131P2 cangive rise to La—O dipoles for HK gate dielectric layers 128N1-128N2 and128P1-128P2 doped with La or La₂O₃ dopants. Dipole concentrations D1-D2in dipole layers 131N1-131N2 depend on the dopant concentrations nearand/or at HKN1-ION1 and HKN2-ION2 interfaces. Similarly, dipoleconcentrations D4-D5 in dipole layers 131P1-131P2 depend on the dopantconcentrations near and/or at HKP1-IOP1 and HKP2-IOP2 interfaces. Dipoleconcentrations D3 and D6 in NFET 102N3 and PFET 102P3 can be equal tozero because of the undoped HK gate dielectric layers 128N3 and 128P3,respectively. The dipole concentration refers to the amount of dipoleper unit volume. In some embodiments, the dipoles from dipole layers131N1-131N2 can have a polarity similar to a polarity of the dipolesfrom dipole layers 131P1-131P2. In some embodiments, the dipoles fromdipole layers 131N1-131N2 can have a polarity opposite to a polarity ofthe dipoles from dipole layers 131P1-131P2, when different dopants areused in NFETs and PFETs.

As shown in FIGS. 1J-1M, dipole concentrations D1-D6 in dipole layers131N1-131N3 and 131P1-131P3 can be proportional to EWF values E1-E6 andthreshold voltages V1-V6 of NFETs 102N1-102N3 and PFETs 102P1-102P3.Thus, controlling the dopant concentrations near and/or at HKN1-ION1 andHKN2-ION2 interfaces can adjust EWF values E1-E2 and absolute values ofthreshold voltages V1-V2. Similarly, controlling the dopantconcentrations near and/or at HKP1-IOP1 and HKP2-IOP2 interfaces canadjust EWF values E4-E5 and absolute values of threshold voltages V4-V5.

Referring to FIGS. 1B-1C, first dopant control layers 129 can beconfigured to control the dopant concentration profiles across HK gatedielectric layers 128N1 and 128P1 and across HKN1-ION1 and HKP1-IOP1interfaces and in interfacial oxide layers 127N1 and 127P1. Seconddopant control layers 130 can be configured to control the dopantconcentration profiles across HK gate dielectric layers 128N2 and 128P2and across HKN2-ION2 and HKP2-IOP2 interfaces and in interfacial oxidelayers 127N2 and 127P2. The discussion of first and second dopantcontrol layers 129-130 applies to both NFETs and PFETs, unless mentionedotherwise. In some embodiments, first and second dopant control layers129-130 can include Si and based on the concentration of Si in each offirst and second dopant control layers 129-130, the dopant concentrationprofiles across HK gate dielectric layers 128N1-128N2 and acrossHKN1-ION1 and HKN2-ION2 interfaces and across interfacial oxide layers127N1-127N2 can be adjusted.

As shown in FIG. 1N, decreasing Si concentration in first dopant controllayer 129 can increase the dopant concentration at the HKN1-ION1interface or in the top portion of interfacial oxide layer and candecrease the dopant concentration between HK gate dielectric layer 128N1and first dopant control layer 129 or across the HK gate dielectriclayer 128N1. Similarly, decreasing Si concentration in second dopantcontrol layer 130 can increase the dopant concentration at HKN2-ION2interface or in the top portion of interfacial oxide layer and candecrease the dopant concentration between HK gate dielectric layer 128N2and second dopant control layer 130 or across the HK gate dielectriclayer 128N2. In some embodiments, increasing or decreasing the Siconcentration in first control layer 129 with respect to the Siconcentration in IO layer 127N1 can decrease or increase the dopantconcentration across the HKN1-ION1 interface because of the chemicalaffinity between Si and dopants of HK gate dielectric layer 128N1.Similarly, the dopant concentration across the HKN2-ION2 interface canbe increased or decreased by decreasing or increasing the Siconcentration in second control layer 130 with respect to the Siconcentration in IO layer 127N2.

Thus, the dopant concentration profiles of each NFET and/or PFET can beadjusted independently of each other by varying the Si concentration infirst and second dopant control layers 129-130. Referring to FIG. 1O,the dopant concentration profiles along lines C-C and D-D of FIGS. 1B-1Ccan be different from each other by having Si concentrations in firstand second dopant control layers 129-130 different from each other. Insome embodiments, first dopant control layer 129 has a lower Siconcentration than second dopant control layer 130. As a result, dopantconcentration is higher at the HKN1-ION1 interface than at HKN2-ION2interface as shown in FIG. 1O. The dopant concentration profiles of FIG.1O can be achieved with each HK gate dielectric layers 128N1-128N2and/or 128P1-128P2 doped with a total amount of dopants (or a dopantdosage) similar to each other before the deposition of first and seconddopant control layers 129-130. That is, the dopant concentrationprofiles in the gate structures 112N1 and in the gate structure 112N2are similar to each other (not shown) before the deposition of first andsecond dopant control layers 129-130. In some embodiments, Si of firstand second dopant control layers 129-130 can diffuse depths DP1-DP2 intoHK gate dielectric layers 128N1-128N2, respectively, as shown in FIG.1O. In some embodiments, depth DP1 can range from about 0.01 nm to about0.3 nm, and depth DP2 can range from about 0.8 nm to about 1.5 nm. Insome embodiments, Si concentration within depth DP1 can range from about0 atomic % to about 5 atomic % and Si concentration within depth DP2 canrange from about 5 atomic % to about 30 atomic % with respect to otherelements in HK gate dielectric layers 128N1-128N2.

In some embodiments, first dopant control layer 129 can have titaniumsilicon nitride (TiSiN) with about 0 atomic % (e.g., TiN) to about 30atomic % of Si with respect to Ti, and second dopant control layer 130can have TiSiN with about 30 atomic % to about 100 atomic % (e.g., SiN,or pure Si) of Si with respect to Ti. In some embodiments, second dopantcontrol layer 130 can have a Si to metal atomic concentration ratiogreater than a Si to metal atomic concentration ratio of first dopantcontrol layer 129. In some embodiments, a ratio of Si concentration insecond control layer 130 to Si concentration in IO layer 127N2 isgreater than a ratio of Si concentration in first control layer 129 toSi concentration in IO layer 127N1.

In some embodiments, first and second dopant control layers 129 and 130can have substantially constant Si concentrations A and B along linesC-C and D-D as shown in FIGS. 1P and 1Q, respectively, whereconcentration A is lower than concentration B. In some embodiments,first and second dopant control layers 129 and 130 can have graded Siconcentration profiles along lines C-C and D-D as shown in FIGS. 1P and1Q, respectively. In some embodiments, first and second dopant controllayers 129 and 130 can have step-shaped Si concentration profiles alonglines C-C and D-D as shown in FIGS. 1T and 1U, respectively, where a topportion of first dopant control layer 129 has a higher Si concentrationthan its bottom portion and a top portion of second dopant control layer130 has a lower Si concentration than its bottom portion. Siconcentration C of bottom portion of first dopant control layer 129 canbe lower than Si concentration D of bottom portion of second dopantcontrol layer 130 as shown in FIGS. 1T-1U. In some embodiments, firstand/or second dopant control layers 129-130 can have TiSiN, Si, SiO₂,silicon titanium (SiTi), Ge, SiGe, tantalum silicide (TaSi₂), titaniumsilicide (TiSi₂), nickel silicide (NiSi), tungsten silicide (WSi₂),molybdenum silicide (MoSi₂), or a combination thereof.

In some embodiments, HK gate dielectric layers 128N1-128N2 can be dopedwith a total amount of dopants (or a dopant dosage) different from eachother, and a dopant control layer 133 can be used to achieve differentdipole concentrations in dipole layers 131N1-131N2 as shown in FIG. 1F,which is a portion 100A of the structure of FIG. 1B. In someembodiments, dopant control layer 133 can be similar to first or seconddopant control layers 129-130. In some embodiments, first and seconddopant control layers 129-130 can be removed from gate structures112N1-112N3 to form the structures of FIG. 1G after desired dopantconcentration profiles are achieved across the HKN1-ION1 and HKN2-ION2interfaces. FIG. 1G shows a portion 100A of the structure of FIG. 1Bwith first and second dopant control layers 129-130 removed. Also, FIG.1G shows gate structures 112N1-112N2 can be formed without WFM layers132N when threshold voltages of NFETs and PFETs can be adjusted withdopant control layers, such as dopant control layers 129-130. In someembodiments, gate structures 112N1-112N2 of FIG. 1B can be formedwithout WFM layers 132N similar to gate structures 112N1-112N2 of FIG.1G. The dopant concentration profiles along lines C*-C* and D*-D* ofFIG. 1G can be similar to the dopant concentration profiles shown inFIG. 1O within the HK gate dielectric region and IO region.

In some embodiments, HK gate dielectric layers 128N1-128N2 and128P1-128P2 can be initially doped with a total amount of dopants (or adopant dosage) similar to each other, and subsequently different dopantcontrol layers 129-130 can be used to achieve different dipoleconcentrations in dipole layers 131N1-131N2 and 131P1-131P2. In someembodiments, first and second dopant control layers 129-130 can beremoved from gate structures 112N1-112N3 and 112P1-112P3 to form thestructures of FIGS. 1V-1W after desired dopant concentration profilesare achieved across the HKN1-ION1, HKN2-ION2, HKP1-IOP1, and HKP2-IOP2interfaces. FIGS. 1V-1W show the structures of FIGS. 1B-1C with firstand second dopant control layers 129-130 removed. The dopantconcentration profiles along lines C-C and D-D of FIGS. 1V-1W can besimilar to the dopant concentration profiles shown in FIG. 1O within theHK gate dielectric region and IO region. In some embodiments, gatestructures 112N1-112N2 and 112P1-112P2 can be formed with WFM layers132N-132P when threshold voltages of NFETs and PFETs needs to be furtheradjusted with dopant control layers, such as dopant control layers129-130, together with WFM layers 132N-132P.

In some embodiments, NFETs 102N1-102N4 can have gate structures112N1*-112N4* with cross-sectional views (along line A-A of FIG. 1A) asshown in FIG. 1H. The discussion of gate structure 112N1-112N2 appliesto respective gate structures 112N4*-112N3*, unless mentioned otherwise.The discussion of HK gate dielectric layer 128N1-128N2 applies torespective HK gate dielectric layer 128N1*-128N2* and the discussion ofdipole layer 131N1-131N2 applies to respective dipole layers131N1*-131N2*, unless mentioned otherwise. Each gate structures 112N4*and 112N2* have a total amount of dopants greater than a total amount ofdopants of gate structures 112N1* and 112N3*, respectively. Dipoleconcentrations in dipole layers 131N1* and 131N2 are greater than dipoleconcentrations in dipole layers 131N1 and 131N2*, respectively. In someembodiments, PFETs 102P1-102P4 can have gate structures 112P1*-112P4*with cross-sectional views (along line B-B of FIG. 1A) as shown in FIG.1I. The discussion of gate structure 112P1-112P2 applies to respectivegate structures 112P4*-112P3*, unless mentioned otherwise. Thediscussion of HK gate dielectric layer 128N1*-128N2* and dipole layers131N1*-131N2* applies to HK gate dielectric layer 128P1*-128P2* anddipole layers 131P1*-131P2*, respectively.

Referring back to FIG. 1B-1E, in some embodiments, WFM layers 132N caninclude titanium aluminum (TiAl), titanium aluminum carbide (TiAlC),tantalum aluminum (TaAl), tantalum aluminum carbide (TaAlC), or acombination thereof and WFM layers 132P can include substantiallyTi-based nitrides or alloys, such as TiN, TiSiN, WN, WCN, Ru, W, Mo anda combination thereof. A glue layer is often deposited after WFM layer132N or 132P and before depositing FFW layer 134. The glue layer caninclude TiN, Ti, Co or a combination thereof. FFW layers 134 can preventany substantial diffusion of fluorine (e.g., no fluorine diffusion) fromfluorine-based precursors used during the deposition of overlying gatemetal fill layers 135 to underlying layers. FFW layers 134 can includesubstantially fluorine-free tungsten layers. In some embodiments, FFWlayer can be absent or not deposited at all. Gate metal fill layers 135can include a suitable conductive material, such as W, Ti, silver (Ag),ruthenium (Ru), molybdenum (Mo), copper (Cu), cobalt (Co), Al, iridium(Ir), nickel (Ni), metal alloys, and a combination thereof. Gate spacers114 and inner spacers 142 can form sidewalls of gate structures112N1-112N3 and 112P1-112P3. Each of gate spacers 114 and inner spacer142 can include insulating material, such as silicon oxide, siliconnitride, silicon oxynitride, a low-k material, and a combinationthereof.

Semiconductor device 100 can further include isolation structure 104,etch stop layer (ESL) 116, interlayer dielectric (ILD) layer 118, andshallow trench isolation (STI) regions 138. Isolation structure 104 canelectrically isolate NFETs 102N1-102N3 and PFETs 102P1-102P3 from eachother. ESL 116 can be configured to protect gate structures 112N1-112N3and 112P1-112P3 and/or S/D regions 110A-110B. In some embodiments,isolation structure 104 and ESL 116 can include an insulating material,such as silicon oxide and silicon germanium oxide. ILD layer 118 can bedisposed on ESL 116 and can include a dielectric material. STI regions138 can be configured to provide electrical isolation between NFETs102N1-102N3 and PFETs 102P1-102P3 and can include an insulatingmaterial.

The cross-sectional shapes of semiconductor device 100 and its elements(e.g., fin structure 108 ₁-108 ₂, gate structures 112N1-112N3 and112P1-112P3, epitaxial fin regions 110A-110B, inner spacers 142, gatespacers 114, and/or STI regions 138) are illustrative and are notintended to be limiting.

FIG. 2 is a flow diagram of an example method 200 for fabricatingsemiconductor device 100, according to some embodiments. Forillustrative purposes, the operations illustrated in FIG. 2 will bedescribed with reference to the example fabrication process forfabricating semiconductor device 100 as illustrated in FIGS. 3A-12B.FIGS. 3A-12B are cross-sectional views along lines A-A and B-B ofsemiconductor device 100 at various stages of fabrication, according tosome embodiments. FIGS. 6C and 11C-11D illustrate dopant concentrationprofiles along lines E-E and F-F of semiconductor device 100 at variousstages of its fabrication process, in accordance with some embodiments.Operations can be performed in a different order or not performeddepending on specific applications. It should be noted that method 200may not produce a complete semiconductor device 100. Accordingly, it isunderstood that additional processes can be provided before, during, andafter method 200, and that some other processes may only be brieflydescribed herein. Elements in FIGS. 3A-12B with the same annotations aselements in FIGS. 1A-1I are described above.

In operation 205, polysilicon structures and epitaxial fin regions areformed on fin structures of NFETs and PFETs. For example, as shown inFIGS. 3A-3B, polysilicon structures 312 can be formed on fin structures108 ₁-108 ₂ and gate spacers 114 can be formed on sidewalls ofpolysilicon structures 312. During subsequent processing, polysiliconstructures 312 can be replaced in a gate replacement process to formgate structures 112N1-112N3 and 112P1-112P3. Following the formation ofgate spacers 114, n- and p-type epitaxial fin regions 110A-110B can beselectively formed on portions of fin structures 108 ₁-108 ₂ that arenot underlying polysilicon structures 312. After the formation ofepitaxial fin regions 110A-110B, ESL 116 and ILD 118 can be formed toform the structures of FIGS. 3A-3B.

Referring to FIG. 2, in operation 210, gate openings are formed on andwithin the one or more fin structures. For example, as shown in FIGS.4A-4B, gate openings 412N-412P associated with NFETs 102N1-102N3 andPFETs 102P1-102P3, respectively, can be formed on and within finstructures 108 ₁-108 ₂. The formation of gate openings 412N can includesequential operations of (i) etching polysilicon structures 312 from thestructures of FIGS. 3A-3B, and (ii) etching nanostructured regions 122Nand 120P from the structures of FIGS. 3A-3B.

Referring to FIG. 2, in operations 215-235, gate-all-around (GAA)structures are formed in the gate openings. For example, based onoperations 215-235, gate structures 112N1-112N3 and 112P1-112P3 can bewrapped around nanostructured channel regions 120N and 122P, asdescribed with reference to FIGS. 5A-12B.

In operation 215, interfacial oxide layers and an HK gate dielectriclayer are deposited and annealed within the gate openings. For example,as shown in FIGS. 5A-5B, interfacial oxide layers 127N1-127N3 and127P1-127P3 and a HK gate dielectric layer 128 can be deposited andannealed on nanostructured channel regions 120N and 122P within gateopenings 412N-412P of FIGS. 4A-4B. During subsequent processing, HK gatedielectric layer 128 can form HK gate dielectric layers 128N1-128N3 and128P1-138P3 of FIGS. 1A-1E. FIGS. 5A-5B show portions 100A-100B of thestructures of FIGS. 4A-4B, respectively, for the sake of clarity.

Interfacial oxide layers 127N1-127N3 and 127P1-127P3 can be formed onexposed surfaces of nanostructured channel regions 120N and 122P withingate openings 412N-412P. In some embodiments, interfacial oxide layers127 can be formed by exposing nanostructured channel regions 120N and122P to an oxidizing ambient. The oxidizing ambient can include acombination of ozone (O₃), a mixture of ammonia hydroxide, hydrogenperoxide, and water (“SC1 solution”), and/or a mixture of hydrochloricacid, hydrogen peroxide, water (“SC2 solution”).

The deposition of HK gate dielectric layer 128 can include blanketdepositing HK gate dielectric layer 128 on the partial semiconductordevice 100 (not shown) formed after the formation of interfacial oxidelayers 127. The blanket deposited HK gate dielectric layer 128 can besubstantially conformally deposited on interfacial oxide layers 127 andthe exposed surfaces of the partial semiconductor device 100 as shown inFIGS. 5A-5B. In some embodiments, HK gate dielectric layer 128 can beformed with ALD using hafnium chloride (HfCl₄) as a precursor at atemperature ranging from about 250° C. to about 350° C. In someembodiments, gate dielectric layer 128 can have a thickness ranging fromabout 1 nm to about 3 nm in order to wrap around nanostructures channelregions 120N and 122P without being constrained by spacing betweenadjacent nanostructured channel regions 120N and between adjacentnanostructured channel regions 122P.

Referring to FIG. 2, in operation 220, a doping process is selectivelyperformed on the HK gate dielectric layer portions of the first NFETsand PFETs and second NFETs and PFETs. For example, as shown in FIGS.6A-6B, portions of HK gate dielectric layer 128 of NFETs 102N1-102N2 andPFETs 102P1-102P2 can be doped with metal dopants that induces theformation of dipole layers 631N1-631N2 and 631P1-631P2. Duringsubsequent processing, dipole layers 631N1-631N2 and 631P1-631P2 canform dipole layers 131N1-131N2 and 131P1-131P2 of FIGS. 1A-1E. Thedoping process can include sequential operations of (i) blanketdepositing a dopant source layer (not shown) on the structures of FIGS.5A-5B, (ii) patterning the dopant source layer to form patterned dopantsource layer 640 as shown in FIGS. 6A-6B, (iii) performing a drive-inanneal process on the structures of FIGS. 6A-6B, and (iv) removingdopant source layer 640. This doping process can dope the portions of HKgate dielectric layer 128 in 102N1, 102N2, and in 102P1, 102P2 as shownin FIG. 6A-6B with a similar amount of dopants because the same dopantsource layer is used. It should be noted that, at this stage the dopantconcentration profiles across lines E-E and F-F in 112N1-112N2 and112P1-112P2 are similar to each other.

The blanket deposition of the dopant source layer can include blanketdepositing about 0.05 nm to about 2 nm thick dopant source layer on HKgate dielectric layer 128 with an ALD or a CVD process. The dopantsource layer can include (i) an oxide of rare-earth metals, such asLanthanum oxide (La₂O₃), Yttrium oxide (Y₂O₃), Cerium oxide (CeO₂),Ytterbium oxide (Yb₂O₃), Erbium oxide (Er₂O₃), Scandium oxide (Sc₂O₃)and Lutetium oxide (Lu₂O₃); (ii) an oxide of a metal from group IIA(e.g., magnesium oxide (MgO) or strontium oxide (SrO)), group IIIA(e.g., aluminum oxide (Al₂O₃)), group IIIB (e.g., yttrium oxide (Y₂O₃)),or group IVB (e.g., zirconium oxide (ZrO₂) or titanium oxide (TiO₂)) ofthe periodic table; or (iii) a combination thereof. The patterning ofthe dopant source layer can include using lithography and etchingprocesses that include acid-based (e.g., HCl-based) chemical etching orchemicals including HCl, H₂O₂, NH₄OH, HF, H₃PO₄, DI water or acombination thereof.

The drive-in anneal process can include annealing dopant source layer640 at a temperature from about 550° C. to about 850° C. and at apressure from about 1 torr to about 50 torr for a time period rangingfrom about 0.1 second to about 30 seconds. In some embodiments, thedrive-in anneal process can include two anneal processes: (i) a soakanneal process at a temperature from about 550° C. to about 850° C. fora time period ranging from about 2 sec to about 60 sec and (ii) a spikeanneal process at a temperature from about 700° C. to about 900° C. fora time period ranging from about 0.1 second to about 2 seconds. FIG. 6Cshows dopant concentration profiles along lines E-E and F-F of FIGS.6A-6B after patterning of dopant source layer 640 and after the drive-inanneal process. Following the drive-in anneal process, the dopantconcentration increases at the HK-IO interfaces of NFETs 102N1-102N2 andPFETs 102P1-102P2 and can have graded profiles across dipole layers631N1-631N2 and 631P1-631P2 as shown in FIG. 6C.

In some embodiments, instead of the doping process described withreference to FIGS. 6A-6B, portions of HK gate dielectric layer 128 ofNFETs 102N1-102N2 and PFETs 102P1-102P2 can be doped with the processdescribed with reference to FIGS. 7A-7B to dope the portions of HK gatedielectric layer 128 with different amount of dopants. The dopingprocess can include sequential operations of (i) blanket depositing afirst dopant source layer (not shown) on the structures of FIGS. 5A-5B,(ii) patterning the first dopant source layer to form a patterned firstdopant source layer 740 as shown in FIGS. 7A-7B, (iii) blanketdepositing a second dopant source layer (not shown) on the structuresformed after the patterning of the first dopant source layer, (iv)patterning the second dopant source layer to form a patterned seconddopant source layer 742 as shown in FIGS. 7A-7B, (iii) performing adrive-in anneal process on the structures of FIGS. 7A-7B, and (iv)removing first and second dopant source layers 740 and 742. Optionally,the doping process can be followed by deposition of a thin high-kdielectric layer similar to HK gate dielectric layer 128 on doped HKgate dielectric layer 128.

The first and second dopant source layers 740 and 742 can be similar toor different from each other in material composition and can includematerial similar to dopant source layer 640. The drive-in anneal processcan be similar to that described with reference to FIGS. 6A-6B. Portionsof HK gate dielectric layer 128 underlying the stack of first and seconddopant source layers 740 and 742 can be doped with a larger amount ofdopants than portions of HK gate dielectric layer underlying seconddopant source layer 742. As a result, dipole layers 731N1-731P1 inducedby the dopants from the stack of first and second dopant source layers740 and 742 can have a higher dipole concentration than dipole layers731N2-731P2 induced by the dopants from second dopant source layers 740.

In some embodiments, instead of the doping process in HK gate dielectriclayer 128, as described with reference to FIGS. 6A-6B and 7A-7B, IOlayers 127N1-127N3 and 127P1-127P3 of NFETs 102N1-102N2 and PFETs102P1-102P2 can be doped with different amount of dopants prior to thedeposition of HK gate dielectric layer 128 as shown in FIGS. 7C-7D. Thedoping process of IO layers 127N1-127N3 and 127P1-127P3 can be similarto the doping process of HK gate dielectric layer 128 described withreference to FIGS. 7A-7B.The doping process of IO layers 127N1-127N3 and127P1-127P3 can include sequential operations of (i) blanket depositinga first dopant source layer (not shown) on IO layers 127N1-127N3 and127P1-127P3, (ii) patterning the first dopant source layer to form apatterned first dopant source layer 740 as shown in FIGS. 7C-7D, (iii)blanket depositing a second dopant source layer (not shown) on thestructures formed after the patterning of the first dopant source layer,(iv) patterning the second dopant source layer to form a patternedsecond dopant source layer 742 as shown in FIGS. 7C-7D, (iii) performinga drive-in anneal process on the structures of FIGS. 7C-7D toincorporate dopant into top portions of IO layers 127N1-127N3 and127P1-127P3, and (iv) removing first and second dopant source layers 740and 742. The doping process of IO layers 127N1-127N3 and 127P1-127P3 canbe followed by the deposition of HK gate dielectric layer 128 as shownin FIGS. 7E-7F. The deposition of HK gate dielectric layer 128 of FIGS.7E-7F can be similar to the deposition process of HK gate dielectriclayer 128 described with reference to FIGS. 5A-5B.

Referring to FIG. 2, in operation 230, dopant concentration profilesacross the doped portions of the HK gate dielectric layer are adjusted.For example, as illustrated with reference to FIGS. 8A-11B and 11C-11D,dopant concentration profiles across HK gate dielectric layer 128 can beadjusted using first and second dopant control layers 129*-130*, atwo-stage annealing process, and a Si capping layer 1144. The dopantconcentration profile adjusting process can include sequentialoperations of: (i) forming first and second dopant control layers129*-130* (as shown in FIGS. 8A-9B) on the structures of FIGS. 6A-6Bafter removing dopant source layer 640 (or on the structures of FIGS.7A-7B after removing dopant source layers 740 and 742 or on thestructures of FIGS. 7E-7F), (ii) performing a first anneal process onthe structures of FIGS. 9A-9B as shown in FIGS. 10A-10B, (iii) blanketdepositing Si capping layer 1144 on the first annealed structures ofFIGS. 10A-10B as shown in FIGS. 11A-11B, (iv) performing a second annealprocess on the structures of FIGS. 11A-11B, and (v) removing Si cappinglayer 1144. In some embodiments, first and second dopant control layers129*-130* can be removed (not shown) after removing Si capping layer1144.

The process for forming first and second dopant control layers 129*-130*can include sequential operations of (i) blanket depositing a firstdopant control layer (not shown) on the structures of FIGS. 6A-6B afterremoving dopant source layer 640 (or on the structures of FIGS. 7A-7Bafter removing dopant source layers 740 and 742), (ii) patterning thefirst dopant control layer to form patterned first dopant control layer129* as shown in FIGS. 8A-8B, and (iii) blanket depositing second dopantcontrol layer 130* on the structures of FIGS. 8A-8B as shown in FIGS.9A-9B. After the formation of dopant control layers 129*-130, the dopantconcentration profiles across gate structures 112N1-112N2 are similar toeach other and the dopant concentration profiles across gate structures112P1-112P2 are similar to each other (not shown). During subsequentprocessing, first and second dopant control layers 129*-130* can formfirst and second dopant control layers 129-130 of FIGS. 1A-1E.

The blanket deposition of the first and second dopant control layers129*-130* can include blanket depositing about 0.8 nm to about 5 nmthick materials for the first and second dopant control layers 129*-130*on HK gate dielectric layer 128 with an ALD or a CVD process. Thematerials for first and second dopant control layers 129*-130* caninclude TiSiN, Si, SiO₂, SiTi, Ge, SiGe, TaSi₂, TiSi₂, NiSi, WSi₂,MoSi₂, TiN or a combination thereof. In some embodiments, the blanketdepositing of first dopant control layer 129* can include depositing aTiSiN layer with about 0 atomic % (e.g., TiN) to about 30 atomic % of Siwith respect to Ti. The blanket depositing of second dopant controllayer 130* can include depositing a TiSiN layer with about 30 atomic %to about 100 atomic % (e.g., SiN) of Si with respect to Ti.

To deposit the TiSiN layers with such Si concentrations in first andsecond dopant control layers 129*-130* that are different from eachother, the TiSiN deposition processes can include using Si precursors,Ti precursors, and N precursors at a temperature ranging from about 300°C. to about 550° C. In some embodiments, Si precursor can include Silane(SiH₄), Disilane (Si₂H₆), Dichlorosilane (SiH₂Cl₂), Hexachlorodisilane(Si₂Cl₆), Dimethyl dichlorosilane (Si(CH₃)₂Cl₂), TEOS (Si(OC₂H₅)₄),Trichlorosilane (SiHCl₃), Trichloro disilane (Si₂H₃Cl₃), Hexa-methyldisilane ((Si(CH₃)₃)₂), or Tetra-ethyl silane (Si(C₂H₅)₄). In someembodiments, Ti precursor can include Titanium tetrachloride (TiCl₄),TDMAT-Tetrakis-dimethylamido-titanium(Ti(N(CH₃)₂)₄), orTDMADT-tris(dimethylamido)-(dimethylamino-2-propanolato)titanium(Ti(NMe₂)₃(dmap)). In some embodiments, N precursor can include Ammonia(NH₃), Hydrazine (N₂H₄), Forming gas (N₂+H₂), NH₃, N₂,H₂ plasma, orcracked ammonia. In some embodiments, the TiSiN layers for first andsecond dopant control layers 129*-130* can be deposited using TiCl₄,SiH₄, and NH₃ at a temperature ranging from about 400° C. to about 460°C.

The first annealing process can include performing a isothermal soakingannealing at a temperature of about 500° C. to about 700° C. followed bya spike annealing process on the structures of FIGS. 9A-9B in a nitrogenambient at an annealing temperature ranging from about 850° C. to about900° C. for a time period ranging from about 1 second to about 5seconds. The blanket deposition of Si capping layer 1144 can includedepositing a silicon-based layer with a thickness of about 2 nm to about5 nm on second dopant control layer 130* by an ALD, a CVD, or a PVDprocess using SiH₄, disaline (Si₂H₆), and hydrogen at a temperatureranging from about 350° C. to about 450° C. The second annealing processcan include performing a spike annealing process in a nitrogen ambientat an annealing temperature (e.g., about 900° C. to about 950° C.)higher than that of the first annealing process for a time periodranging from about 1 second to about 10 seconds. FIGS. 11C-11Dillustrate the changes in the dopant concentration profiles along linesE-E and F-F of FIGS. 9A-11B at various stages of the adjusting process.

FIG. 11E illustrates the dopant concentration profiles along lines E-Eand F-F of FIGS. 11A-11B after the adjusting process. After theformation of dopant control layers 129*-130* as shown in FIGS. 9A-9B,the dopant concentration profiles across gate structures 112N1-112N2 aresimilar to each other and the dopant concentration profiles across gatestructures 112P1-112P2 are similar to each other (not shown). Howeverafter operation 230, the dopant concentration profiles across gatestructure 112N1-112N2 are different from each other and the dopantconcentration profiles across gate structures 112P1-112P2 are differentfrom each other as shown in FIG. 11E. Thus different dipole controllayers, such as dopant control layers 129*-130* can be used to formdifferent dopant concentration profiles in different devices. In someembodiments, these different dipole control layers can remain in gatestructures as shown FIGS. 1B-1C. In some embodiments, the differentdipole control layers can be removed from gate structures as shown FIGS.1V-1W and have dopant concentration profiles as shown in FIG. 11E.

Referring to FIG. 2, in operation 235, WFM layers, glue layers, FFWlayers, and gate metal fill layers are formed on the second dopantcontrol layer if the first and second dopant control layers are notremoved in operation 230 or formed on HK dielectric layer 128 if thefirst and second dopant control layers are removed. For example, asshown in FIGS. 12A-12B, WFM layers 132N-132P, glue layers (not shown),FFW layers 134, and gate metal fill layers 135 can be formed on thestructures of FIGS. 11A-11B. The materials for WFM layers 132N-132P canbe blanket deposited on the structures of FIGS. 11A-11B. The materialfor FFW layers 134 can be blanket deposited on the material for WFMlayers 132N-132P. The material for gate metal fill layers 135 can beblanket deposited on the material for FFW layers 134. Following theseblanket depositions, HK gate dielectric layer 128, first and seconddopant control layers 129*-130*, the materials for WFM layers 132N-132P,the material for FFW layers 134, and the material for gate metal filllayers 135 can be polished by a chemical mechanical polishing process toform the structures of FIGS. 12A-12B. Thus, as described in operations215-235, gate structures 112N1-112N3 and 112P1-112P3 can be formed withat least three different threshold voltages on the same substrate 106.

The present disclosure provides example multi-Vt devices with FETs(e.g., GAA FETs and/or finFETs) having threshold voltages different fromeach other and provides example methods of forming such FETs on the samesubstrate. The example methods form NFETs and PFETs with WFM layer ofsimilar thicknesses or without WFM layers, but with different thresholdvoltages on the same substrate. These example methods can be morecost-effective (e.g., cost reduced by about 20% to about 30%) andtime-efficient (e.g., time reduced by about 15% to about 20%) inmanufacturing reliable FET gate structures with different thresholdvoltages than other methods of forming FETs with similar channeldimensions and threshold voltages on the same substrate. In addition,these example methods can form FET gate structures with smallerdimensions (e.g., thinner gate stacks) than other methods of formingFETs with similar threshold voltages. Furthermore these example methodscan form FET gate structures with improved device performance (e.g.,lower flicker noise, higher k value, lower CET, higher speed etc.).

In some embodiments, multiple NFETs and PFETs with different gatestructure configurations, but with similar WFM layer thicknesses, andwith similar overall total dopant dosage can be selectively formed onthe same substrate to achieve threshold voltages different from eachother. The different gate structures can have same initial amount oftotal overall dopant dosage (obtained by similar dopant source layerthicknesses on different gate structures as shown in 102N1, 102N2 inFIG. 6A). These different gate structures can then have different dopantcontrol layers of different compositions disposed and patterned onhigh-K (HK) gate dielectric layers. The different dopant control layerscan provide different concentration profiles of metal dopants in the HKgate dielectric layers and at HK-IO interfaces of the different gatestructure. The different metal dopant concentration profiles can inducedipoles of different concentrations at HK-IO interfaces. The differentdipole concentrations result in gate structures with different EWFvalues, threshold voltages and flat band voltage shifts. Thus, tuningthe composition of the dopant control layers can tune the EWF values ofthe NFET and PFET gate structures and, as a result, can adjust thethreshold voltages of the NFETs and PFETs without varying their WFMlayer thicknesses or even without varying the initial total dopantdosage amount in their gate structure. Also the different metal dopantconcentration profiles can induce different dopant concentrations in HKgate dielectric layers. The different dopant concentration in HK gatedielectric layers result in different k-values of HK gate dielectriclayers, different CET values and different charge scattering anddifferent flicker noise performance. Thus, tuning the composition ofdopant layer can also tune the NFET and PFET device performance.

In some embodiments, a method includes forming first and second gateopenings on a fin structure, forming first and second interfacial oxide(IO) layers within the first and second gate openings, respectively,depositing a high-K (HK) gate dielectric layer with first and secondlayer portions within the first and second gate openings, respectively,performing a doping process with a metal-based dopant on the first andsecond layer portions, selectively forming a first dopant control layerwith a first Si concentration on the first layer portion, and depositinga second dopant control layer with a second Si concentration on thesecond layer portion. The second Si concentration is greater than thefirst Si concentration. The method further includes adjusting first andsecond dopant concentration profiles across the first and second layerportions, respectively, such that a first interface between the firstlayer portion and the first IO layer has a first dopant concentrationand a second interface between the second layer portion and the secondIO layer has a second dopant concentration that is smaller than thefirst dopant concentration and depositing a gate metal fill layer on thefirst and second layer portions.

In some embodiments, a method includes forming first and secondinterfacial oxide (IO) layers on a fin structure, depositing a high-K(HK) gate dielectric layer with first and second layer portions on thefirst and second IO layers, respectively, depositing a first dopantsource layer on the first layer portion, depositing a second dopantsource layer with a first portion on the first dopant source layer and asecond portion on the second layer portion, removing the first andsecond dopant source layers, selectively forming a first dopant controllayer on the first layer portion, depositing a second dopant controllayer with a silicon (Si)-to-metal atomic concentration ratio greaterthan a Si-to-metal atomic concentration ratio of the first dopantcontrol layer, and depositing a gate metal fill layer on the seconddopant control layer.

In some embodiments, a semiconductor device includes a substrate, a finstructure disposed on the substrate, and first and second gatestructures on the fin structure. The first and second gate structuresincludes first and second interfacial oxide (IO) layers, respectively,first and second high-K (HK) gate dielectric layers disposed on thefirst and second IO layers, respectively, and first and second dopantcontrol layers disposed on the first and second HK gate dielectriclayers, respectively. The second dopant control layer has a silicon(Si)-to-metal atomic concentration ratio greater than an Si-to-metalatomic concentration ratio of the first dopant control layer. Thesemiconductor device further includes first and second work functionmetal layers disposed on the first and second dopant control layers,respectively, and first and second gate metal fill layers disposed onthe first and second work function metal layers, respectively.

The foregoing disclosure outlines features of several embodiments sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodimentsintroduced herein. Those skilled in the art should also realize thatsuch equivalent constructions do not depart from the spirit and scope ofthe present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A method, comprising: forming first and secondgate openings on a fin structure; forming first and second interfacialoxide (IO) layers within the first and second gate openings,respectively; depositing a high-K (HK) gate dielectric layer with firstand second layer portions within the first and second gate openings,respectively; performing a doping process with a metal-based dopant onthe first and second layer portions; adjusting first and second dopantconcentration profiles across the first and second layer portions,respectively, such that a first interface between the first layerportion and the first IO layer has a first dopant concentration and asecond interface between the second layer portion and the second IOlayer has a second dopant concentration that is smaller than the firstdopant concentration, wherein the adjusting comprises: selectivelyforming a first dopant control layer with a first Si concentration onthe first layer portion; depositing a second dopant control layer with asecond Si concentration on the second layer portion, wherein the secondSi concentration is greater than the first Si concentration; anddepositing a gate metal fill layer on the first and second layerportions.
 2. The method of claim 1, wherein the selectively forming thefirst dopant control layer comprises: depositing a layer of silicon(Si)-based material on the first and second layer portions; andselectively etching portions of the layer of Si-based material on thesecond layer portion.
 3. The method of claim 1, wherein the adjustingthe first and second dopant concentration profiles comprises depositinga Si capping layer on the first and second dopant control layers.
 4. Themethod of claim 1, wherein the adjusting the first and second dopantconcentration profiles comprises: performing a first isothermal soakannealing process at a first soak temperature; performing a first spikeannealing process at a first temperature; and performing a second spikeannealing process at a second temperature higher than the firsttemperature.
 5. The method of claim 1, wherein the adjusting the firstand second dopant concentration profiles comprises: performing a firstannealing process at a first temperature after the depositing the seconddopant control layer; depositing a Si capping layer on the first andsecond dopant control layers after the first annealing process; andperforming a second annealing process at a second temperature higherthan the first temperature after the depositing the Si capping layer. 6.The method of claim 1, further comprising removing the first and seconddopant control layers after the adjusting the first and second dopantconcentration profiles.
 7. The method of claim 1, wherein the depositingthe second dopant control layer comprises depositing a layer of Si- andmetal-based material with an Si-to-metal atomic concentration ratiogreater than an Si-to-metal atomic concentration ratio of the firstdopant control layer.
 8. The method of claim 1, wherein the selectivelyforming the first dopant control layer comprises depositing a firsttitanium silicon nitride (TiSiN) layer with about 0 atomic % to about 30atomic % of Si with respect to Ti, and wherein the depositing the seconddopant control layer comprises depositing a second TiSiN layer withabout 30 atomic % to about 100 atomic % of Si with respect to Ti.
 9. Themethod of claim 1, wherein the doping process comprising doping thefirst layer portion with a first dopant concentration and doping thesecond layer portion with a second dopant concentration that is greaterthan the first dopant concentration.
 10. The method of claim 1, whereinthe first and second dopant control layers comprise titanium siliconnitride layers of different Si-to-Titanium atomic concentration ratio.11. The method of claim 1, wherein the performing the doping processcomprises: depositing a dopant metal-based layer on the first and secondlayer portions; performing a drive-in anneal process on the dopantmetal-based layer; and removing the dopant metal-based layer with wetetching.
 12. The method of claim 1, wherein the performing the dopingprocess comprises: depositing a rare-earth metal-based layer on thefirst and second layer portions; soak annealing the rare-earthmetal-based layer at a first temperature from about 550° C. to about800° C.; and spike annealing the rare-earth metal-based layer at asecond temperature from about 700° C. to about 900° C.; and removing theremaining dopant metal based layer residue from top of first and secondlayer portions with wet etching chemicals.
 13. A method, comprising:forming first and second interfacial oxide (IO) layers on a finstructure; depositing a first dopant source layer on the first IO layer;depositing a second dopant source layer with a first portion on thefirst dopant source layer and a second portion on the second IO layer;removing the first and second dopant source layers; depositing a high-K(HK) gate dielectric layer with first and second layer portions on thedoped first and second IO layers, respectively; selectively forming afirst dopant control layer on the first layer portion; depositing asecond dopant control layer with a silicon (Si)-to-metal atomicconcentration ratio greater than a Si-to-metal atomic concentrationratio of the first dopant control layer; and depositing a gate metalfill layer on the second dopant control layer.
 14. The method of claim13, further comprising performing a drive-in anneal process after thedepositing the second dopant source layer.
 15. The method of claim 13,further comprising adjusting first and second dopant concentrationprofiles across the first and second layer portions, respectively, suchthat a first interface between the first layer portion and the first IOlayer has a first dopant concentration and a second interface betweenthe second layer portion and the second IO layer has a second dopantconcentration that is greater than the first dopant concentration. 16.The method of claim 13, further comprising performing an annealingprocess after the depositing the second dopant control layer.
 17. Asemiconductor device, comprising: a substrate; a fin structure disposedon the substrate; and first and second gate structures on the finstructure, wherein the first and second gate structures comprise: firstand second interfacial oxide (IO) layers, respectively; first and secondhigh-K (HK) gate dielectric layers disposed on the first and second IOlayers, respectively; first and second dopant control layers disposed onthe first and second HK gate dielectric layers, respectively, whereinthe second dopant control layer has a silicon (Si)-to-metal atomicconcentration ratio greater than an Si-to-metal atomic concentrationratio of the first dopant control layer; first and second work functionmetal layers disposed on the first and second dopant control layers,respectively; and first and second gate metal fill layers disposed onthe first and second work function metal layers, respectively.
 18. Thesemiconductor device of claim 17, wherein a first interface between thefirst HK gate dielectric layer and the first IO layer has a first dopantconcentration and a second interface between the second HK gatedielectric layer and the second IO layer has a second dopantconcentration that is smaller than the first dopant concentration. 19.The semiconductor device of claim 17, wherein the dopant concentrationin the first HK gate dielectric layer is smaller than the dopantconcentration in the second HK gate dielectric layer.
 20. Thesemiconductor device of claim 17, wherein a first concentration of Si ina top portion of the first HK gate dielectric layer is smaller than asecond concentration of Si in a top portion of the second HK gatedielectric layer.